Adhesive film, optical member comprising the same, and optical display apparatus comprising the same

ABSTRACT

An adhesive film, an optical member including the same, and an optical display apparatus including the same are provided. An adhesive film is formed of an adhesive composition including a (meth)acrylic copolymer, a curing agent, a mono- or higher functional monomer, a binder having a melting point of about 30° C. to about 60° C., and an initiator, and has a peel strength increase rate of 7.0 or more, as calculated according to Equation 1 herein.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to and the benefit of Korean PatentApplication No. 10-2021-0037616, filed on Mar. 23, 2021 in the KoreanIntellectual Property Office, the entire disclosure of which isincorporated herein by reference.

BACKGROUND 1. Field

Aspects of embodiments of the present invention relate to an adhesivefilm, an optical member including the same, and an optical displayapparatus including the same.

2. Description of the Related Art

In recent years, optical displays using organic light emitting diodes(OLED) have been developed. In particular, an optical display based onflexible organic light emitting diodes has been spotlighted in the art.

A flexible panel based on flexible organic light emitting diodesincludes a plastic film, such as a polyimide film and the like, on eachof upper and lower sides of the panel. The flexible panel is moreflexible than a liquid crystal panel and a typical organic lightemitting diode-based panel. Accordingly, a protective film for processesis temporarily adhered to the flexible panel to protect the flexiblepanel or to prevent or substantially prevent occurrence of scratches onthe flexible panel during a process of processing, assembling, and/orinspecting the flexible panel. When it is determined through inspectionof the flexible panel that there is a defect, such as abnormalappearance or foreign matter, it is desirable for the protective film tohave low peel strength in order to be easily removed from the flexiblepanel. After inspection of the flexible panel, a protective film forreinforcement is adhered to the flexible panel to support the panelwhile protecting the panel from external environments. Therefore, theprotective film for reinforcement is desired to have higher peelstrength and reliability than the protective film for processes.

However, in a typical panel manufacturing process, a process ofassembling a temporary protective film for processes to a panel, aprocess of peeling off the temporary protective film of the panel, and aprocess of assembling a protective film for reinforcement to the panelmust be sequentially performed, thereby complicating the manufacturingprocess. Moreover, since the protective film for processes must bediscarded after the peeling process, there is a problem of deteriorationin economic efficiency and environmental friendliness.

The background technique of the present invention is disclosed in JPPatent Registration No. 5,683,369 and the like.

SUMMARY

According to an aspect of one or more embodiments of the presentinvention, an adhesive film is provided that can be easily removed froman adherend after attachment of the adhesive film thereto and can besecured to the adherend through a process (e.g., a predeterminedprocess).

According to another aspect of one or more embodiments of the presentinvention, an adhesive film is provided that can be adhered at low peelstrength to an adherend to provide temporary protection to the adherendin an initial stage and can be easily removed therefrom withoutdeformation and/or damage to the adherend through selective cutting ofan unnecessary portion of the adhesive film.

According to another aspect of one or more embodiments of the presentinvention, a protective adhesive film is provided that exhibitssignificant increase in peel strength after irradiation with light andheat treatment, as compared with peel strength before irradiation withlight, and is secured to an adherend to improve durability of an opticalmember including the adherend.

According to another aspect of one or more embodiments of the presentinvention, an adhesive film is provided that can be concurrently (e.g.,simultaneously) used as a temporary protective film for processes withrespect to a flexible panel substrate and as a protective film forreinforcement of patterns, which is selectively partially peeled off toform patterns.

According to an aspect of one or more embodiments of the presentinvention, an adhesive film is provided.

According to one or more embodiments, an adhesive film is formed of anadhesive composition including a (meth)acrylic copolymer, a curingagent, a mono- or higher functional monomer, a binder having a meltingpoint of about 30° C. to about 60° C., and an initiator, and has a peelstrength increase rate of 7.0 or more, as calculated by the followingEquation 1:

Peel strength increase rate=P2/P1,

where P1 is an initial peel strength (unit: gf/inch) of the adhesivefilm with respect to an adherend, as measured on a specimen of theadhesive film and the adherend, and P2 is a peel strength of theadhesive film (unit: gf/inch) with respect to the adherend, as measuredon the specimen of the adhesive film and the adherend after irradiationwith light and heat treatment of the specimen.

According to one or more embodiments, an adhesive film is formed of anadhesive composition including a (meth)acrylic copolymer, a curingagent, a mono- or higher functional monomer, a binder having a meltingpoint of about 30° C. to about 60° C., and an initiator, and has aninitial peel strength of greater than 0 gf/inch to about 100 gf/inchwith respect to an adherend, as measured on a specimen of the adhesivefilm and the adherend, and a peel strength of 500 gf/inch or more withrespect to the adherend, as measured on the specimen of the adhesivefilm and the adherend after irradiation and heat treatment of thespecimen.

In one or more embodiments, P1 may be greater than 0 gf/inch and lessthan or equal to about 100 gf/inch.

In one or more embodiments, P2 may be about 500 gf/inch or more.

In one or more embodiments, the mono- or higher functional monomer mayhave a higher glass transition temperature in a homopolymer phase thanthe (meth)acrylic copolymer.

In one or more embodiments, a difference in glass transition temperaturebetween the mono- or higher functional monomer in a homopolymer phaseand the (meth)acrylic copolymer may be about 20° C. or more.

In one or more embodiments, the mono- or higher functional monomer mayhave a glass transition temperature of about −30° C. or more in ahomopolymer phase.

In one or more embodiments, the mono- or higher functional monomer mayinclude an aromatic group-containing mono- or higher functional monomer.

In one or more embodiments, the aromatic group-containing mono- orhigher functional monomer may include a compound of the followingFormula 1:

where R¹ is hydrogen or a methyl group; s is an integer of 0 to 10; R²is a substituted or unsubstituted C₆ to C₅₀ aryl group or a substitutedor unsubstituted C₆ to C₅₀ aryloxy group; and T is a substituted orunsubstituted C₁ to C₆ alkylene group or a substituted or unsubstitutedC₁ to C₆ alkyleneoxy group.

In one or more embodiments, the mono- or higher functional monomer maybe present in an amount of about 10 parts by weight to about 200 partsby weight relative to 100 parts by weight of the (meth)acryliccopolymer.

In one or more embodiments, the (meth)acrylic copolymer may have a glasstransition temperature of about −10° C. or less.

In one or more embodiments, the (meth)acrylic copolymer may include acopolymer of a monomer mixture including an alkyl group-containing(meth)acrylic monomer and a hydroxyl group-containing (meth)acrylicmonomer, and the hydroxyl group-containing (meth)acrylic monomer may bepresent in an amount of about 0.1 mol % to about 10 mol % in the monomermixture.

In one or more embodiments, the curing agent may include a mixture of anisocyanate curing agent and a metal chelate curing agent.

In one or more embodiments, the binder having a melting point of about30° C. to about 60° C. may include a binder of a monomer mixtureincluding a (meth)acrylate having a linear or branched C₁₆ to C₂₂ alkylgroup at an ester site.

In one or more embodiments, the monomer mixture may further include atleast one selected from among a (meth)acrylate having a linear orbranched alkyl group containing ten or fewer carbon atoms at an estersite and a silicone-modified mono-functional (meth)acrylate.

In one or more embodiments, the initiator may include at least oneselected from among a photo-radical initiator and a photo-cationicinitiator.

In one or more embodiments, the adhesive composition may include 100parts by weight of the (meth)acrylic copolymer, about 0.01 parts byweight to about 8 parts by weight of the curing agent, about 10 parts byweight to about 200 parts by weight of the mono- or higher functionalmonomer, about 0.1 parts by weight to about 20 parts by weight of thebinder having a melting point of about 30° C. to about 60° C., and about0.01 parts by weight to about 7.5 parts by weight of the initiator.

According to another aspect of one or more embodiments of the presentinvention, an optical member is provided.

According to one or more embodiments, an optical member includes aflexible panel and the adhesive film according to an embodiment of thepresent invention stacked on at least one surface of the flexible panel.

In one or more embodiments, the optical member may include the flexiblepanel including a flexible substrate, the adhesive film stacked on alower surface of the flexible substrate, and a protective film stackedon a lower surface of the adhesive film.

According to another aspect of one or more embodiments of the presentinvention, an optical display apparatus including the adhesive filmaccording to an embodiment of the present invention is provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a view of a specimen for measurement of T-peel strength; and

FIG. 1B is a view of the specimen in measurement of T-peel strength.

DETAILED DESCRIPTION

Herein, some embodiments of the present invention will be described infurther detail. However, it is to be understood that the presentinvention is not limited to the following embodiments and may beembodied in different ways. The following embodiments are provided toprovide a thorough understanding of the invention to those skilled inthe art.

Herein, “(meth)acryl” refers to acryl and/or methacryl.

Herein, “copolymer” may include a polymer or a resin.

Herein, “binder” refers to a compound having a lower weight averagemolecular weight than an adhesive polymer or an adhesive resin, forexample, a weight average molecular weight of about 10,000 g/mol toabout 100,000 g/mol.

Herein, “glass transition temperature” may refer to a glass transitiontemperature (Tg) measured on a target compound using a DSC Discovery (TAInstruments). Specifically, a homopolymer of a target monomer is heatedto about 180° C. at a heating rate of about 20° C./min, is slowly cooledto about −100° C., and is heated again to about 100° C. at a heatingrate of 10° C./min to obtain data of an endothermic transition curve. Aninflection point of the endothermic transition curve may be defined asthe glass transition temperature of a target monomer in a homopolymerphase.

Herein, “melting point” may refer to a melting point (Tm) measured usinga DSC Discovery (TA Instruments). Specifically, a target binder isheated to about 180° C. at a heating rate of about 20° C./min, is slowlycooled to about −100° C., and is heated again to about 100° C. at aheating rate of 10° C./min to obtain data of an endothermic transitioncurve. An inflection point of the endothermic transition curve may bedefined as the melting point of the target binder.

Herein, “peel strength” may refer to T-peel strength.

As used herein to represent a specific numerical range, the expression“X to Y” means a value greater than or equal to X and less than or equalto Y (X≤ and ≤Y).

An adhesive film according to embodiments of the present invention is anadhesive film having low peel strength (initial peel strength) and notsubjected to irradiation with light and heat treatment. The adhesivefilm according to embodiments of the present invention exhibits asuitable range of peel strength before irradiation with light. Thus, theadhesive film can be adhered at low peel strength to an adherend toprovide temporary protection to the adherend and can be easily removedtherefrom without deformation and/or damage to the adherend.Accordingly, the adhesive film according to embodiments of the presentinvention can be used as a temporary protective film for processes withrespect to a flexible panel substrate, e.g., a flexible OLED panelsubstrate. In terms of this feature, the adhesive film according toembodiments of the present invention is distinguished from a coat forformation of an adhesive film, which exhibits no peel strength beforeirradiation with light upon formation of the adhesive film using atypical photo-curable adhesive composition, in which the coat does nothave a function of temporarily protecting the adherend.

In an embodiment, the adhesive film according to the present inventionhas an initial peel strength of greater than 0 gf/inch to about 100gf/inch, and, in an embodiment, 0.1 gf/inch, 5 gf/inch, 10 gf/inch, 15gf/inch, 20 gf/inch, 25 gf/inch, 30 gf/inch, 35 gf/inch, 40 gf/inch, 45gf/inch, 50 gf/inch, 55 gf/inch, 60 gf/inch, 65 gf/inch, 70 gf/inch, 75gf/inch, 80 gf/inch, 85 gf/inch, 90 gf/inch, 95 gf/inch, or 100 gf/inch,for example, about 10 gf/inch to about 100 gf/inch, about 20 gf/inch toabout 70 gf/inch, or about 30 gf/inch to about 70 gf/inch. The initialpeel strength may be realized by an adhesive composition including a(meth)acrylic copolymer, a curing agent, a mono- or higher functionalmonomer, a binder having a melting point (Tm) of about 30° C. to about60° C., and an initiator. These components will be described in furtherdetail below.

The adhesive film according to embodiments of the present inventionexhibits significant increase in peel strength after irradiation withlight and heat treatment, as compared with peel strength beforeirradiation with light. Since the adhesive film according to the presentinvention exhibits significant increase in peel strength afterirradiation with light and heat treatment, the adhesive film is adheredto an adherend to provide permanent protection to the adherend, therebyimproving durability of an optical member including the adherend towhich the adhesive film is adhered.

Accordingly, the adhesive film according to embodiments of the presentinvention can achieve both temporary protection and permanent protectionwith respect to an adherend and can be used as a temporary protectivefilm for processes and a protective film for reinforcement, therebyenabling process simplification, economic feasibility and environmentalfriendliness. The temporary protective film for processes may be a filmthat is temporarily adhered to the adherend and then removed therefromto temporarily protect the adherend. The protective film forreinforcement may be a film that is permanently adhered to the adherendto protect the adherend from external environments and is not removedfrom the adherend.

The adhesive film according to embodiments of the present invention issubjected to irradiation with light and heat treatment in order toimprove peel strength with respect to the adherend, in which thesequence of irradiation with light and heat treatment is notparticularly limited. That is, the adhesive film may be sequentiallysubjected to irradiation with light and heat treatment, or vice versa.In an embodiment, the adhesive film is sequentially subjected toirradiation with light and heat treatment to achieve effective increasein peel strength.

The adhesive film according to embodiments of the present invention canbe used as a protective film for reinforcement. The protective film forreinforcement refers to a protective film that is stacked on at leastone surface of a flexible panel and protects the flexible panel fromexternal impact.

In addition, the adhesive film according to embodiments of the presentinvention can be used as a protective film for reinforcement ofpatterns, which is stacked on a flexible panel and is then selectivelypartially peeled off to form patterns on the remaining adhesive film.

Herein, “adherend” refers to a plastic film, for example, a polyimidefilm, a polycarbonate film, a polyester film, such as a polyethylenenaphthalate film, a polyethylene terephthalate film, and the like, apolyether sulfone film, and a polyurethane film. In an embodiment, theadherend is a polyimide film.

The polyimide film is a polymer film prepared through polymerization ofa polyamic acid acting as a precursor and containing an imide group andan aromatic group in a repeat unit, and has good mechanical propertiesto be broadly used as a substrate of a flexible OLED panel.

Herein, an adhesive film according to one or more embodiments of thepresent invention will be described.

The adhesive film according to one or more embodiments of the presentinvention (herein referred to as “adhesive film”) has a peel strengthincrease rate of 7.0 or more, as calculated by the following Equation 1.Within this range, the adhesive film can be adhered to an adherend withhigh peel strength and high reliability after irradiation with light andheat treatment to provide a bonding effect with respect to the adherendand can be used as a protective film for reinforcement:

Peel strength increase rate=P2/P1,  Equation 1

where P1 is an initial peel strength (unit: gf/inch) of the adhesivefilm with respect to an adherend, as measured on a specimen of theadhesive film and the adherend, and P2 is a peel strength of theadhesive film (unit: gf/inch) with respect to the adherend, as measuredon the specimen of the adhesive film and the adherend after irradiationwith light and heat treatment of the specimen.

In an embodiment, the peel strength increase rate of Equation 1 is in arange of about 7.0 to about 200, and, in an embodiment, 7.0, 8, 10, 20,30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180,190, or 200, and, in an embodiment, about 10 to about 50, and, in anembodiment, about 10 to about 20. Within this range, the adhesive filmcan easily secure suitable initial peel strength and suitable peelstrength after irradiation and heat treatment.

In an embodiment, the adhesive film may have a P1 value (initial peelstrength) of greater than 0 gf/inch to about 100 gf/inch, and, in anembodiment, 0.1 gf/inch, 5 gf/inch, 10 gf/inch, 15 gf/inch, 20 gf/inch,25 gf/inch, 30 gf/inch, 35 gf/inch, 40 gf/inch, 45 gf/inch, 50 gf/inch,55 gf/inch, 60 gf/inch, 65 gf/inch, 70 gf/inch, 75 gf/inch, 80 gf/inch,85 gf/inch, 90 gf/inch, 95 gf/inch, or 100 gf/inch, for example, about10 gf/inch to about 100 gf/inch, about 20 gf/inch to about 70 gf/inch,or about 30 gf/inch to about 70 gf/inch. Within this range, the adhesivefilm can be easily removed from an adherend without deformation and/ordamage to the adherend and allows easy increase in peel strength afterirradiation with light.

In an embodiment, the adhesive film may have a P2 value of about 500gf/inch or more, and, in an embodiment, 500 gf/inch, 550 gf/inch, 600gf/inch, 650 gf/inch, 700 gf/inch, 750 gf/inch, 800 gf/inch, 850gf/inch, 900 gf/inch, 950 gf/inch, 1,000 gf/inch, 1,050 gf/inch, 1,100gf/inch, 1,150 gf/inch, 1,200 gf/inch, 1,250 gf/inch, 1,300 gf/inch,1,350 gf/inch, 1,400 gf/inch, 1,450 gf/inch, 1,500 gf/inch, 1,550gf/inch, 1,600 gf/inch, 1,650 gf/inch, 1,700 gf/inch, 1,750 gf/inch,1,800 gf/inch, 1,850 gf/inch, 1,900 gf/inch, 1,950 gf/inch, or 2,000gf/inch, for example, about 500 gf/inch to about 2,000 gf/inch, about700 gf/inch to about 2,000 gf/inch, or about 500 gf/inch to about 1,000gf/inch. Within this range, the adhesive film can be adhered to anadherend with high peel strength and high reliability, thereby providingeffective protection to the adherend.

Here, P2 is a value measured on a specimen of the adhesive film and theadherend after irradiation with light and heat treatment. According toembodiments of the present invention, despite physical change of theadhesive film due to improvement in cohesive strength and/or modulus ofthe adhesive film after irradiation with light and heat treatment anddespite curing of the mono- or higher functional monomer by irradiationwith light, shrinkage of the adhesive film is suppressed, and the binderhaving a melting point of about 30° C. to about 60° C. is allowed todiffuse on the surface of the adherend due to heat treatment and heatgenerated upon curing of the mono- or higher functional monomer byirradiation of the adhesive film with light, thereby improving peelstrength of the adhesive film after irradiation with light and heattreatment. When the mono- or higher functional monomer is cured byirradiation with light, a typical adhesive film suffers fromdeterioration in peel strength through curing shrinkage, whereasshrinkage of the adhesive film according to embodiments of the presentinvention is suppressed even after irradiation with light. This featurewill be described in further detail below.

Herein, “irradiation with light” may include irradiation of the adhesivefilm with light having a wavelength of about 280 nm to about 430 nm, forexample, 280 nm, 290 nm, 300 nm, 310 nm, 320 nm, 330 nm, 340 nm, 350 nm,360 nm, 370 nm, 380 nm, 390 nm, 400 nm, 410 nm, 420 nm, or 430 nm, and,in an embodiment, in the range of about 350 nm to about 390 nm, and at adose of about 1,000 mJ/cm². UV irradiation may be performed using atleast one of a UV LED, a high pressure mercury lamp, and a metal halidelamp.

Herein, “heat treatment” may include a process of leaving the adhesivefilm at a temperature higher than or equal to the melting point of thebinder, for example, at a temperature of about 40° C. to about 60° C.,for about 5 minutes to about 30 minutes.

The adhesive film according to the present invention is formed of anadhesive composition including a (meth)acrylic copolymer, a curingagent, a mono- or higher functional monomer, a binder having a meltingpoint of about 30° C. to about 60° C., and an initiator.

In an embodiment, the adhesive film may have the mono- or higherfunctional monomer, the binder having a melting point of about 30° C. toabout 60° C., and the initiator dispersed in a matrix of the adhesivefilm formed by curing the (meth)acrylic copolymer and the curing agentwith heat.

(Meth)Acrylic Copolymer

The (meth)acrylic copolymer forms the matrix of the adhesive film and iscured by the curing agent to provide initial peel strength of theadhesive film. After irradiation with light, the (meth)acrylic copolymercan assist in improvement of modulus and cohesive strength of theadhesive film together with the mono- or higher functional monomer andthe binder having a melting point of about 30° C. to about 60° C.

In an embodiment, the (meth)acrylic copolymer may have a glasstransition temperature (Tg) of about −10° C. or less, and, in anembodiment, −70° C., −65° C., −60° C., −55° C., −50° C., −45° C., −40°C., −35° C., −30° C., −25° C., or −20° C., for example, about −60° C. toabout −20° C. Within this range, the (meth)acrylic copolymer can assistin securing wettability (adhesive strength) of the adhesive film withrespect to an adherend and initial peel strength of the adhesive filmand can increase peel strength after irradiation with light throughadjustment of the glass transition temperature together with the mono-or higher functional monomer and the binder having a melting point ofabout 30° C. to about 60° C.

In an embodiment, the (meth)acrylic copolymer may have a weight averagemolecular weight of about 500,000 g/mol or more, and, in an embodiment,500,000 g/mol, 600,000 g/mol, 700,000 g/mol, 800,000 g/mol, 900,000g/mol, 1,000,000 g/mol, 1,100,000 g/mol, 1,200,000 g/mol, 1,300,000g/mol, 1,400,000 g/mol, or 1,500,000 g/mol, for example, about 600,000g/mol to about 1,500,000 g/mol. Within this range, the (meth)acryliccopolymer can assist in securing wettability (adhesive strength) andinitial peel strength of the adhesive film with respect to an adherendand can increase peel strength of the adhesive film.

In an embodiment, the (meth)acrylic copolymer may include a copolymer ofa monomer mixture including an alkyl group-containing (meth)acrylicmonomer and a hydroxyl group-containing (meth)acrylic monomer.

The alkyl group-containing (meth)acrylic monomer serves to form thematrix of the adhesive film and may include an unsubstituted C₁ to C₂₀alkyl group-containing (meth)acrylic acid ester. For example, the alkylgroup-containing (meth)acrylic monomer may include at least one selectedfrom among methyl (meth)acrylate, ethyl (meth)acrylate, propyl(meth)acrylate, n-butyl (meth)acrylate, t-butyl (meth)acrylate,iso-butyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate,heptyl (meth)acrylate, ethylhexyl (meth)acrylate, octyl (meth)acrylate,iso-octyl (meth)acrylate, nonyl (meth)acrylate, decyl (meth)acrylate,and lauryl (meth)acrylate.

In an embodiment, the alkyl group-containing (meth)acrylic monomer maybe present in an amount of about 85 mol % to about 99.5 mol %, and, inan embodiment, about 90 mol % to about 98 mol %, or about 95 mol % toabout 99 mol %, in the monomer mixture. Within this range, the adhesivefilm can exhibit good wettability (adhesive strength) with respect to anadherend and can secure suitable initial peel strength.

The hydroxyl group-containing (meth)acrylic monomer may be a(meth)acrylate containing at least one hydroxyl group. For example, thehydroxyl group-containing (meth)acrylate may be a (meth)acrylic acidester containing a C₁ to C₂₀ alkyl group having at least one hydroxylgroup, a (meth)acrylic acid ester containing a C₅ to C₂₀ cycloalkylgroup having at least one hydroxyl group, or a (meth)acrylic acid estercontaining a C₆ to C₂₀ aryl group having at least one hydroxyl group.The hydroxyl group-containing (meth)acrylate may include at least oneselected from among 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl(meth)acrylate, 4-hydroxybutyl (meth)acrylate, hydroxyhexyl(meth)acrylate, 1,4-cyclohexanedimethanol mono(meth)acrylate,1-chloro-2-hydroxypropyl (meth)acrylate, diethyleneglycolmono(meth)acrylate, 1,6-hexanediol mono(meth)acrylate, pentaerythritoltri(meth)acrylate, dipentaerythritol penta(meth)acrylate, neopentylglycol mono(meth)acrylate, trimethylol propane di(meth)acrylate,trimethylol ethane di(meth)acrylate, 2-hydroxy-3-phenyloxypropyl(meth)acrylate, 4-hydroxycyclopentyl (meth)acrylate, 4-hydroxycyclohexyl(meth)acrylate, and cyclohexane dimethanol mono(meth)acrylate.

In an embodiment, the hydroxyl group-containing (meth)acrylic monomermay be present in an amount of about 0.1 mol % to about 10 mol %, and,in an embodiment, 0.1 mol %, 0.5 mol %, 1 mol %, 1.5 mol %, 2 mol %, 2.5mol %, 3 mol %, 3.5 mol %, 4 mol %, 4.5 mol %, 5 mol %, 5.5 mol %, 6 mol%, 6.5 mol %, 7 mol %, 7.5 mol %, 8 mol %, 8.5 mol %, 9 mol %, 9.5 mol%, or 10 mol %, for example, about 0.5 mol % to about 10 mol %, and, inan embodiment, about 2 mol % to about 10 mol %, and, in an embodiment,about 1 mol % to about 5 mol %, in the monomer mixture. Within thisrange, the adhesive composition can impart cohesive strength to anadhesive layer to form the adhesive layer and can secure suitableinitial peel strength of the adhesive film.

The monomer mixture may further include a carboxylic acid-containingmonomer. The carboxylic acid-containing monomer can assist in securinginitial adhesive strength through improvement in cohesive strengthbetween the (meth)acrylic binder and the curing agent. The carboxylicacid-containing monomer may include (meth)acrylic acid, without beinglimited thereto.

In an embodiment, the carboxylic acid-containing monomer may be presentin an amount of about 0.05 mol % to about 5 mol %, and, in anembodiment, 0.05 mol %, 0.1 mol %, 0.5 mol %, 1 mol %, 1.5 mol %, 2 mol%, 2.5 mol %, 3 mol %, 3.5 mol %, 4 mol %, 4.5 mol %, or 5 mol %, forexample, about 0.1 mol % to about 5 mol %, in the monomer mixture.Within this range, the adhesive composition can impart cohesive strengthto an adhesive layer to form the adhesive layer and can secure suitableinitial peel strength of the adhesive film.

In an embodiment, the monomer mixture may include a (meth)acrylicmonomer, which has a glass transition temperature of about −80° C. ormore, and, in an embodiment, −80° C., −75° C., −70° C., −65° C., −60°C., −55° C., −50° C., −45° C., −40° C., −35° C., −30° C., −25° C., −20°C., −15° C., −10° C., −5° C., or 0° C., for example, about −80° C. toabout 0° C., and, in an embodiment, about −60° C. to about −20° C., in ahomopolymer phase. Within this range, the monomer mixture can easilyform a (meth)acrylic copolymer having a glass transition temperaturewithin this above range.

The monomer mixture may include at least one selected from among methylacrylate, acrylic acid, and methacrylic acid. With these monomers, the a(meth)acrylic copolymer having a glass transition temperature withinthis above range can be easily prepared.

The (meth)acrylic copolymer may be prepared through typicalpolymerization of the monomer mixture. Polymerization may include atypical method well-known to those skilled in the art. For example, the(meth)acrylic copolymer may be prepared by adding a radical initiator tothe monomer mixture, followed by typical copolymerization, for example,suspension polymerization, emulsion polymerization, solutionpolymerization, and the like. In an embodiment, polymerization may beperformed at about 60° C. to about 70° C. for about 6 hours to about 8hours. The initiator may include a typical initiator including azo-basedpolymerization initiators and/or peroxides, such as benzoyl hydroxide oracetyl hydroxide.

Curing Agent

The curing agent can assist in formation of the matrix of the adhesivefilm through heat curing of the (meth)acrylic copolymer and in securinginitial peel strength of the adhesive film.

The curing agent may be a heat curing agent and may include at least oneselected from among an isocyanate curing agent, a metal chelate curingagent, a carbodiimide curing agent, an aziridine curing agent, and anepoxy curing agent. In an embodiment, an isocyanate curing agent or amixture of an isocyanate curing agent and a metal chelate curing agentis used. The mixture of these curing agents allows easy implementationof the advantageous effects of the present invention.

The isocyanate curing agent may include a bi- or higher functional,specifically bi- to hexa-functional isocyanate curing agent. In anembodiment, the isocyanate curing agent may include at least oneselected from among xylene diisocyanate (XDI) including m-xylenediisocyanate and the like, methylenebis(phenyl isocyanate) (MDI)including 4,4′-methylenebis(phenyl isocyanate) and the like, naphthalenediisocyanate, toluene diisocyanate, hexamethylene diisocyanate, andisophorone diisocyanate, or adducts thereof. For example, the adductsmay include trimethylol propane adducts of toluene diisocyanate,trimethylol propane adducts of hexamethylene diisocyanate, trimethylolpropane adducts of isophorone diisocyanate, trimethylol propane adductsof xylene diisocyanate, isocyanurates of toluene diisocyanate,isocyanurates of hexamethylene diisocyanate, and isocyanurates ofisophorone diisocyanate. The isocyanate curing agent may include atleast one of these compounds.

In an embodiment, the isocyanate curing agent may be present in anamount of about 5 parts by weight or less, and, in an embodiment, 0.001,0.005, 0.1, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, or 5 parts by weight,for example, about 0.001 parts by weight to about 3 parts by weight,and, in an embodiment, about 0.01 parts by weight to about 1 part byweight, relative to 100 parts by weight of the (meth)acrylic copolymer.Within this range, the adhesive composition can improve reliability ofthe adhesive film.

The metal chelate curing agent may include a typical metal chelatecuring agent. For example, the metal chelate curing agent may be acuring agent containing a metal, such as any of aluminum, iron, copper,zinc, tin, titanium, nickel, antimony, magnesium, vanadium, chromium,and zirconium. For example, the metal chelate curing agent may includeat least one selected from among aluminum ethyl acetoacetatediisopropylate, aluminum tris(ethyl acetoacetate), alkyl acetoacetatealuminum diisopropylate, aluminum isopropylate, mono-sec-butoxyaluminumdiisopropylate, aluminum-sec-butyrate, aluminum ethylate,tetra-isopropyl titanate, tetra-normal butyl titanate, butyl titanatedimer, titanium acetyl acetonate, titanium octylene glycolate, titaniumtetra-acetyl acetonate, titanium ethyl acetate, polyhydroxytitaniumstearate, and aluminum acetyl acetonate.

In an embodiment, the metal chelate curing agent may be present in anamount of about 3 parts by weight or less, and, in an embodiment, 0.001,0.005, 0.1, 0.5, 1, 1.5, 2, 2.5, or 3 parts by weight, for example,about 0.001 parts by weight to about 1 part by weight, and, in anembodiment, about 0.01 parts by weight to about 1 part by weight,relative to 100 parts by weight of the (meth)acrylic copolymer. Withinthis range, the metal chelate curing agent can provide additionaleffects without affecting effects of the adhesive film according to thepresent invention.

In an embodiment, the curing agent may be present in an amount of about0.01 parts by weight to about 8 parts by weight, and, in an embodiment,0.01, 0.05, 1, 2, 3, 4, 5, 6, 7, or 8 parts by weight, for example,about 0.01 parts by weight to about 3 parts by weight, and, in anembodiment, about 0.1 parts by weight to about 2 parts by weight,relative to 100 parts by weight of the (meth)acrylic copolymer. Withinthis range, the adhesive composition can improve reliability of theadhesive film.

Mono- or Higher Functional Monomer

The mono- or higher functional monomer has at least one functional groupreacted by an initiator. The functional group may refer to a UV curable,vinyl group or a (meth)acrylate group.

The mono- or higher functional monomer may improve cohesive strengthand/or modulus of the adhesive film after irradiation with light.Accordingly, when the adhesive film adhered to a surface of an adherendis subjected to photocuring, the mono- or higher functional monomerallows the adhesive film to be adhered to the adherend with higher peelstrength, thereby improving peel strength of the adhesive film.

In an embodiment, the mono- or higher functional monomer has two orfewer functional groups. As a result, the mono- or higher functionalmonomer can effectively prevent or substantially prevent excessiveshrinkage of the adhesive film upon curing through irradiation withlight.

It is desirable that a homopolymer of the mono- or higher functionalmonomer have a glass transition temperature in a certain range (e.g., apredetermined range), as compared with the glass transition temperatureof the (meth)acrylic copolymer. As a result, even when the adhesive filmis cured by irradiation with light, shrinkage of the adhesive film issuppressed to improve peel strength of the adhesive film afterirradiation with light.

In an embodiment, a homopolymer of the mono- or higher functionalmonomer has a higher glass transition temperature than the (meth)acryliccopolymer, and a difference in glass transition temperature between themono- or higher functional monomer in a homopolymer phase and the(meth)acrylic copolymer may be about 20° C. or more, and, in anembodiment, 20° C., 25° C., 30° C., 35° C., 40° C., 45° C., 50° C., 55°C., 60° C., 65° C., 70° C., 75° C., 80° C., 85° C., 90° C., 95° C., 100°C., 110° C., 115° C., or 120° C., for example, about 20° C. to about120° C., or about 40° C. to about 100° C. Within this range, the mono-or higher functional monomer can increase peel strength of the adhesivefilm after irradiation with light.

In an embodiment, the mono- or higher functional monomer may have aglass transition temperature of about −30° C. or more, and, in anembodiment, −30° C., −25° C., −20° C., −15° C., −10° C., −5° C., 0° C.,5° C., 10° C., 15° C., 20° C., 25° C., 30° C., 35° C., 40° C., 45° C.,or 50° C., for example, about −30° C. to about 50° C., in a homopolymerphase. Within this range, the homopolymer of the mono- or higherfunctional monomer has a higher glass transition temperature than the(meth)acrylic copolymer, thereby securing increase in peel strength ofthe adhesive film through improvement in cohesive strength afterirradiation with light.

The mono- or higher functional monomer may include a mono- or higherfunctional (meth)acrylate having a linear or branched C₁ to C₂₀ alkylgroup, and, in an embodiment, C₈ to C₂₀ alkyl group, or a linear orbranched C₁ to C₂₀ alkylene group, and, in an embodiment, C₆ to C₂₀alkylene group, at an ester site. For example, the mono- or higherfunctional monomer may include at least one selected from among lauryl(meth)acrylate, stearyl (meth)acrylate, methyl acrylate, n-butylmethacrylate, and 1,6-hexanediol diacrylate.

In an embodiment, the mono- or higher functional monomer may include anaromatic group-containing mono- or higher functional monomer includingat least one aromatic group.

Here, “aromatic group” may refer to a group containing a C₆ to C₅₀monocyclic or heterocyclic ring. For example, the aromatic group maymean a substituted or unsubstituted, phenyl group, a biphenyl group, aterphenyl group, a naphthalenyl group, and the like.

The aromatic group-containing mono- or higher functional monomer helpsimprove adhesive strength of the adhesive film by improving tackiness ofthe adhesive film with respect to an adherend, for example, an aromaticgroup-containing plastic film, and, in an embodiment, a polyimide film,through stacking effects by the π-π bond thereto. In addition, thearomatic group is a bulky substituent, as compared with a linear orbranched alkyl group, and is inserted between a cured network structureof the (meth)acrylic copolymer and the curing agent, for example,between interpenetrating polymer networks (IPNs) or semi-IPNs, beforeirradiation with light, thereby suppressing excessive increase ininitial peel strength of the adhesive film with respect to the adherend.

The aromatic group-containing mono- or higher functional monomer mayinclude a compound of the following Formula 1, without being limitedthereto:

where R¹ is a hydrogen atom or a methyl group; s is an integer of 0 to10; R² is a substituted or unsubstituted C₆ to C₅₀ aryl group or asubstituted or unsubstituted C₆ to C₅₀ aryloxy group; and T is asubstituted or unsubstituted C₁ to C₆ alkylene group or a substituted orunsubstituted C₁ to C₆ alkylene oxy group.

Herein, in “substituted or unsubstituted,” “substituted” means that atleast one hydrogen atom is substituted with a C₁ to C₁₀ alkyl group, aC₁ to C₁₀ thio-alkyl group, a C₁ to C₁₀ alkoxy group, a halogen (F, Cl,Br or I), a C₃ to C₁₀ cycloalkyl group, or a C₆ to C₂₀ aryl group.

In an embodiment, R² may be a substituted or unsubstituted phenoxygroup, phenyl group, benzyl group, biphenyl group, ter-phenyl group, orphenyl phenyl group.

In an embodiment, the aromatic group-containing mono- or higherfunctional monomer may include at least one selected from the groupconsisting of phenoxy (meth)acrylate, phenoxy benzyl (meth)acrylate,2-ethylphenoxy (meth)acrylate, benzyl (meth)acrylate, phenyl(meth)acrylate, 2-ethylthiophenyl (meth)acrylate, 2-phenylethyl(meth)acrylate, 3-phenylpropyl (meth)acrylate, 4-phenylbutyl(meth)acrylate, 2-(2-methylphenyl)ethyl (meth)acrylate,2-(3-methylphenyl)ethyl (meth)acrylate, 2-(4-methylphenyl)ethyl(meth)acrylate, 2-(4-propylphenyl)ethyl (meth)acrylate,2-(4-(1-methylethyl)phenyl)ethyl (meth)acrylate,2-(4-methoxyphenyl)ethyl (meth)acrylate, 2-(4-cyclohexylphenyl)ethyl(meth)acrylate, 2-(2-chlorophenyl)ethyl (meth)acrylate,2-(3-chlorophenyl)ethyl (meth)acrylate, 2-(4-chlorophenyl)ethyl(meth)acrylate, 2-(4-bromophenyl)ethyl (meth)acrylate,2-(3-phenylphenyl)ethyl (meth)acrylate, ortho-biphenyl (meth)acrylate,meta-biphenyl (meth)acrylate, para-biphenyl (meth)acrylate,2,6-terphenyl (meth)acrylate, ortho-terphenyl (meth)acrylate,meta-terphenyl (meth)acrylate, para-terphenyl (meth)acrylate,4-(4-methylphenyl)phenyl (meth)acrylate, 4-(2-methylphenyl)phenyl(meth)acrylate, 2-(4-methylphenyl)phenyl (meth)acrylate,2-(2-methylphenyl)phenyl (meth)acrylate, 4-(4-ethylphenyl)phenyl(meth)acrylate, 4-(2-ethylphenyl)phenyl (meth)acrylate,2-(4-ethylphenyl)phenyl (meth)acrylate, 2-(2-ethylphenyl)phenyl(meth)acrylate, biphenylmethyl (meth)acrylate, naphthyl (meth)acrylate,ethoxylated phenyl (meth)acrylate, ethoxylated phenyl phenol(meth)acrylate, and mixtures thereof.

In an embodiment, the aromatic group-containing mono- or higherfunctional monomer includes at least one selected from among benzyl(meth)acrylate, ethylene glycol phenyl ether acrylate, ethoxylatedphenyl acrylate, ethoxylated phenyl phenol acrylate, phenoxy benzyl(meth)acrylate, biphenyl methyl (meth)acrylate, and naphtyl(meth)acrylates including 1-naphthyl (meth)acrylate, 2-naphthyl(meth)acrylate, and the like.

In an embodiment, the mono- or higher functional monomer may be presentin an amount of about 10 parts by weight to about 200 parts by weight,and, in an embodiment, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65,70, 75, 80, 85, 90, 95, 100, 105, 110, 115, 120, 125, 130, 135, 140,145, 150, 155, 160, 165, 170, 175, 180, 185, 190, 195, or 200 parts byweight, for example, about 30 parts by weight to about 150 parts byweight, and, in an embodiment, about 50 parts by weight to about 120parts by weight, relative to 100 parts by weight of the (meth)acryliccopolymer. Within this range, the adhesive composition can assist inincrease in peel strength of the adhesive film after irradiation withlight and can suppress shrinkage of the adhesive film.

Binder Having a Melting Point of about 30° C. to about 60° C.

The binder having a melting point of about 30° C. to about 60° C. servesto improve peel strength of the adhesive film through heat treatment.The binder having a melting point of about 30° C. to about 60° C. isdiffused on the surface of the adherend through improvement inflowability by heat treatment and heat generated upon curing of a UVcurable monomer by irradiation with light and is crystallized again onthe surface of the adherend to improve peel strength of the adhesivefilm through an anchorage effect when the adhesive film is left at roomtemperature.

The melting point of “30° C. to 60° C.” is set to achieve increase inpeel strength through irradiation with light and heat treatment in theadhesive composition including the (meth)acrylic copolymer, the curingagent, the mono- or higher functional monomer, and the initiator. At amelting point of less than 30° C., since side chains of the binder canbe non-crystallized to have high flowability even before a process(e.g., a predetermined process), the adhesive film has high initial peelstrength, causing deterioration in performance as a temporary protectivefilm. At a melting point of greater than 60° C., the binder does notsuffer from variation in flowability through crystallization of the sidechains of the binder, thereby providing insignificant increase in peelstrength.

In an embodiment, the binder may have a melting point of about 30° C. toabout 60° C., and, in an embodiment, 31° C., 32° C., 33° C., 34° C., 35°C., 36° C., 37° C., 38° C., 39° C., 40° C., 41° C., 42° C., 43° C., 44°C., 45° C., 46° C., 47° C., 48° C., 49° C., 50° C., 51° C., 52° C., 53°C., 54° C., 55° C., 56° C., 57° C., 58° C., 59° C. or 60° C., forexample, about 30° C. to about 50° C., and, in an embodiment, about 30°C. to about 40° C. Within this range, the adhesive film can exhibitbetter increase in peel strength.

The binder may have any suitable composition so long as the binder hasthe above melting point. The binder may be formed of one type of monomeror at least two types of monomers. In an embodiment, the binder isformed of a monomer mixture including at least two monomers in order toeasily reach the melting point according to embodiments of the presentinvention.

For the binder, the monomer mixture may include a (meth)acrylate(herein, “first monomer”) having a linear or branched C₁₆ to C₂₂ alkylgroup at an ester site. In preparation of the binder, the first monomerallows the binder to easily reach the melting point according toembodiments of the present invention. The first monomer may includestearyl (meth)acrylate and/or cetyl (meth)acrylate.

In an embodiment, the first monomer may be present in an amount of 100mol % or less, and, in an embodiment, 70 mol %, 75 mol %, 80 mol %, 85mol %, 90 mol %, or 100 mol %, for example, about 70 mol % to about 100mol %, and, in an embodiment, in a range of about 70 mol % to about 99mol %, about 90 mol % to about 99 mol %, or about 90 mol % to about 100mol %, in the monomer mixture. Within this range, the binder can reachthe melting point according to embodiments of the present invention andcan improve peel strength after heat treatment.

The monomer mixture may further include a monomer (herein, “secondmonomer”), which can form the binder through polymerization with thefirst monomer.

The second monomer may include at least one of a silicone-free monomerthat does not contain silicon and a silicone-based monomer that containssilicon. In an embodiment, the second monomer includes a silicone-basedmonomer.

The silicone-based monomer reduces peel strength of the adhesive filmwith respect to an adherend, improves wettability of the adhesive filmto the adherend, and promotes increase in peel strength by allowing theadhesive film to better permeate the surface of the adhesive film.

The silicone-based monomer may include a silicone-modifiedmono-functional (meth)acrylate. For example, the silicone-based monomermay include a compound of the following Formula 2:

where R₁, R₂, R₃, R₄, R₅, R₆, and R₇ are each independently a hydrogenatom, a C₁ to C₁₀ alkyl group, a C₃ to C₁₀ cycloalkyl group or C₆ to C₁₀aryl group; R₈ is a C₁ to C₁₀ alkylene group or a C₆ to C₁₀ arylenegroup; R₉ is a hydrogen atom or a methyl group; and n is an integer of10 to 100.

In an embodiment, the silicone-based monomer may include a compound ofthe following Formula 3:

where n is an integer of 10 to 100.

The silicone-based monomer may be prepared by a typical method known tothose skilled in the art or obtained from commercially availableproducts.

The silicone-free monomer may include a (meth)acrylate having a linearor branched alkyl group having 10 or fewer carbon atoms, for example, 4to 10 carbon atoms, at an ester site. For example, the silicone-freemonomer may include t-butyl (meth)acrylate and the like.

In an embodiment, the second monomer may be present in an amount ofabout 1 mol % to about 30 mol %, and, in an embodiment, about 1 mol % toabout 10 mol %, in the monomer mixture. Within this range, the bindercan reach the melting point according to embodiments of the presentinvention and can increase peel strength of the adhesive film after heattreatment.

The binder may be prepared using the monomer mixture by a typical methodknown to those skilled in the art.

In an embodiment, the binder having a melting point of about 30° C. toabout 60° C. may be present in an amount of about 0.1 parts by weight toabout 20 parts by weight, and, in an embodiment, 0.1, 0.5, 1, 2, 3, 4,5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20 parts byweight, for example, about 0.5 parts by weight to about 5 parts byweight, relative to 100 parts by weight of the (meth)acrylic copolymer.Within this range, the binder can provide an effect of improving peelstrength of the adhesive film through heat treatment.

Initiator

The initiator serves to allow physical change of the adhesive filmthrough irradiation with light by curing the mono- or higher functionalmonomer. The initiator may include at least one selected from among aphoto-radical initiator and a photo-cationic initiator, and may furtherinclude a heat initiator.

In an embodiment, the initiator may include a photo initiator having amaximum absorption wavelength within an irradiation wavelength rangeapplied to irradiation with light. For example, the photo initiator mayhave a maximum absorption wavelength in a wavelength range of about 280nm to about 430 nm. Within this range, the initiator allows curing ofthe mono- or higher functional monomer through irradiation with light.In an embodiment, the photo initiator may include any of a phosphorusinitiator, a ketone initiator, and the like, without being limitedthereto.

In an embodiment, the initiator may be present in an amount of about0.01 parts by weight to about 7.5 parts by weight, and, in anembodiment, about 0.15 parts by weight to about 4.5 parts by weight,relative to 100 parts by weight of the (meth)acrylic copolymer. Withinthis range, the initiator can secure uniform curing of the mono- orhigher functional monomer through irradiation with light withoutdeterioration in transparency of the adhesive film due to remaininginitiator.

In an embodiment, the initiator may be present in an amount of about0.01 parts by weight to about 5 parts by weight, and, in an embodiment,about 0.5 parts by weight to about 3 parts by weight, relative to 100parts by weight of the mono- or higher functional monomer. Within thisrange, the initiator can secure uniform curing of the mono- or higherfunctional monomer through irradiation with light without deteriorationin transparency of the adhesive film due to remaining initiator.

The adhesive composition may further include a curing accelerator.

The curing accelerator assists in curing reaction of the adhesive filmto further improve cohesive strength of the adhesive layer. The curingaccelerator may include a typical curing accelerator known to thoseskilled in the art. In an embodiment, the curing accelerator may includeany of a tin-based metal compound, a zinc metal compound, an aminecompound, a titanium-based metal compound, a bismuth-based metalcompound, and an aluminum-based metal compound. In an embodiment, amongthese compounds, a tin-based metal compound is used. For example, thecuring accelerator may include tetravalent or divalent organotin-basedcompounds, such as dibutyl tin dilaurate, bis-acetylacetonate-dibutyltin, dibutyl tin dimaleate, and dimaleate tin, withoutbeing limited thereto.

In an embodiment, the curing accelerator may be present in an amount ofabout 0.001 parts by weight to about 3 parts by weight relative to 100parts by weight of the (meth)acrylic copolymer. Within this range, thecuring accelerator can increase the curing rate of the adhesive filmwhile improving cohesive strength of the adhesive film.

The adhesive composition may further include a silane coupling agent.

The silane coupling agent can further increase peel strength of theadhesive film. The silane coupling agent may include a typical silanecoupling agent known to those skilled in the art. For example, thesilane coupling agent may include any of epoxy group-containing silanecoupling agents, such as glycidoxypropyltrimethoxysilane andglycidoxypropylmethyldimethoxysilane, without being limited thereto.

In an embodiment, the silane coupling agent may be present in an amountof about 0.01 parts by weight to about 5 parts by weight relative to 100parts by weight of the (meth)acrylic copolymer. Within this range, thesilane coupling agent can further improve peel strength of the adhesivefilm.

The adhesive composition may further include additives. The additivesmay include typical additives known to those skilled in the art. Forexample, the additives may include at least one selected from amongpigments, UV absorbents, antioxidants, leveling agents, antistaticagents, retarders, and rework agents, without being limited thereto.

The adhesive composition may further include a solvent. The solvent canincrease coatability of the adhesive composition to produce an adhesivefilm having a thin thickness and a uniform surface. The solvent mayinclude typical solvents known to those skilled in the art. For example,the solvent may include any of methyl ethyl ketone, methyl isobutylketone, ethyl acetate, and toluene, without being limited thereto. In anembodiment, the adhesive composition may include a solid content of theadhesive film in 15 wt % to 40 wt %, and, in an embodiment, 20 wt % to30 wt %. Within this range, the adhesive composition can exhibit goodcoatability.

In an embodiment, the adhesive film may have a haze of about 5% or less,specifically about 0.1% to about 2%, and a total luminous transmittanceof about 80% or more, and, in an embodiment, about 85% to about 95%, inthe visible spectrum (for example: in the wavelength range of 380 nm to780 nm). Within this range, the adhesive film has good transparency tobe used in an optical display apparatus.

In an embodiment, an adhesive layer of the adhesive film may have athickness of about 200 μm or less, and, in an embodiment, greater thanabout 0 μm to about 100 μm, and, in an embodiment, about 5 μm to about50 μm. Within this range, the adhesive film can act as a protective filmfor a flexible panel.

An optical member according to one or more embodiments of the presentinvention includes a flexible panel and an adhesive film formed on atleast one surface of the flexible panel, wherein the adhesive filmincludes the adhesive film according to an embodiment of the presentinvention.

An optical member according to an embodiment of the present inventionincludes a flexible panel including a flexible substrate, an adhesivefilm stacked on a lower surface of the flexible substrate, and aprotective film stacked on a lower surface of the adhesive film.

The optical member may include the flexible substrate, the adhesive filmstacked on the lower surface of the flexible substrate, and theprotective film stacked on the lower surface of the adhesive film. In anembodiment, the lower surface of the flexible substrate may be oppositeto a direction in which light is emitted from the flexible panel.

The flexible substrate may serve to support an optical element, such asan organic light emitting diode and the like. The flexible substrate isa plastic film and may include, for example, a polyimide film, apolyester film, such as a polyethylene naphthalate film, a polyethyleneterephthalate film, and the like, a polycarbonate film, a polyethersulfone film, and the like.

The protective layer may be formed of any suitable material so long asthe protective layer is optically clear and can secure flexibility. Forexample, the protective layer may include a protective film including apolyester film, such as a polyethylene naphthalate film, a polyethyleneterephthalate film, and the like, a polycarbonate film, a polyethersulfone film, and the like.

In an embodiment, an optical element may be further stacked on an uppersurface of the flexible substrate. The optical element provides opticalfunctions, for example, light emission, polarization, opticalcompensation, display quality improvement, and/or conductivity, to adisplay apparatus. Examples of the optical element may include an OLEDdevice, a window film, a window, a polarizing plate, a color filter, aretardation film, an elliptical polarizing film, a reflective polarizingfilm, an anti-reflection film, a compensation film, a brightnessenhancing film, an alignment film, a light diffusion film, a glassshatterproof film, a surface protective film, an OLED device barrierlayer, a plastic LCD substrate, and a transparent electrode filmincluding indium tin oxide (ITO), fluorinated tin oxide (FTO),aluminum-doped zinc oxide (AZO), carbon nanotubes (CNT), Ag nanowires,graphene, or the like.

The optical member may be manufactured through modification of a typicalmethod known to those skilled in the art. For example, the opticalmember may be manufactured by preparing a flexible panel including aflexible substrate, bonding a laminate of an adhesive film and aprotective layer to a lower surface of the flexible substrate, andbonding the laminate of the adhesive film and the protective layer tothe flexible panel with high bonding strength through irradiation withlight, when there is no defect, such as appearance abnormality orforeign matter, on the flexible substrate or the flexible panel.However, when there is no defect, such as appearance abnormality orforeign matter, on the flexible substrate or the flexible panel, thelaminate of the adhesive film and the protective layer is removed fromthe flexible panel.

An optical display apparatus according to one or more embodiments of thepresent invention includes an adhesive film according to an embodimentof the present invention.

The optical display apparatus may include an organic light emittingdiode display, a liquid crystal display, and the like. The opticaldisplay apparatus may include a flexible display. However, the opticaldisplay apparatus may include a non-flexible display.

Next, embodiment of the present invention will be described in furtherdetail with reference to some examples. However, it is to be understoodthat these examples are provided for illustration and should not beconstrued in any way as limiting the present invention.

Preparative Example 1

Ethyl acetate was placed as a solvent in a 1 L reactor equipped with acooler for easy temperature regulation under a nitrogen purgingcondition. 100 parts by weight of a monomer mixture including 85 mol %of n-butyl acrylate (BA), 10 mol % of methyl acrylate (MA), 4 mol % of4-hydroxy butyl acrylate (4HBA) and 1 mol % of acrylic acid (AA) wasadded to the reactor. Oxygen was removed from the monomer mixture bysupplying nitrogen gas to the monomer mixture for 30 minutes, followedby maintaining the reactor at 62° C. With the monomer mixture uniformlystirred, 0.08 parts by weight of an initiator (V-601, azo-based radicalinitiator, Wako Chemicals Co., Ltd.) was added thereto and reacted at62° C. for 8 hours, thereby preparing a (meth)acrylic copolymer (weightaverage molecular weight: 1,298,112 g/mol, glass transition temperature:−50° C.). A (meth)acrylic copolymer solution (solid content: 30 wt %)was prepared by adding ethyl acetate as a solvent to the (meth)acryliccopolymer.

Preparative Examples 2 and 3

(Meth)acrylic copolymer solutions were prepared by the same method as inPreparative Example 1 except that the content of each monomer waschanged as listed in Table 1 (unit: mol %). In Table 1, “-” means that acorresponding component was not used.

TABLE 1 Preparative Preparative Preparative Monomer Example 1 Example 2Example 3 BA 85 54 63 MA 10 41 35 4HBA 4 3 2 AA 1 2 — Copolymer Mw1,298,112 1,001,829 662,091 (g/mol) Copolymer Tg −50 −31 −21 (° C.)

Preparative Example 4

Toluene was placed as a solvent in a 1 L reactor equipped with a coolerfor easy temperature regulation under a nitrogen purging condition. 100parts by weight of a monomer mixture including 98 mol % of stearylmethacrylate (STMA) and 2 mol % of silicone acrylate (KF-2012, Shin-EtsuChemical Co., Ltd.) was added to the reactor. Oxygen was removed fromthe monomer mixture by supplying nitrogen gas to the monomer mixture for30 minutes, followed by maintaining the reactor at 70° C. With themonomer mixture uniformly stirred, 0.2 parts by weight of an initiator(V-601, azo-based radical initiator, Wako Chemicals Co., Ltd.) was addedthereto and reacted at 70° C. for 4 hours, thereby preparing a binder(melting point: 38° C.) comprising stearyl methacrylate and siliconeacrylate. A binder solution (solid content: 30 wt %) was prepared byadding toluene as a solvent to the binder.

Preparative Example 5

Toluene was placed as a solvent in a 1 L reactor equipped with a coolerfor easy temperature regulation under a nitrogen purging condition. 100parts by weight of a monomer mixture including 95 mol % of stearylmethacrylate (STMA) and 5 mol % of t-butyl acrylate was added to thereactor. Oxygen was removed from the monomer mixture by supplyingnitrogen gas to the monomer mixture for 30 minutes, followed bymaintaining the reactor at 76° C. With the monomer mixture uniformlystirred, 0.2 parts by weight of an initiator (V-601, azo-based radicalinitiator, Wako Chemicals Co., Ltd.) was added thereto and reacted at76° C. for 4 hours, thereby preparing a binder (melting point: 38° C.)comprising stearyl methacrylate and t-butyl acrylate. A binder solution(solid content: 30 wt %) was prepared by adding toluene as a solvent tothe binder.

Example 1

In terms of solid content, 100 parts by weight of the (meth)acryliccopolymer (Tg: −50° C.) prepared in Preparative Example 1, 0.5 parts byweight of an isocyanate curing agent (TD-75, Soken Co., Ltd.) and 0.3parts by weight of metal chelate curing agent (Hardener M-2, aluminumchelate curing agent, Saiden Co., Ltd.) as curing agents, 0.2 parts byweight of a curing accelerator (accelerator S, tin-based curingaccelerator, Soken Co., Ltd.), 80 parts by weight of lauryl acrylate(Miwon Specialty Chemical Co., Ltd., homopolymer Tg: −23° C.) as amono-functional monomer, 0.5 parts by weight of an initiator (IrgacureTPO, phosphorus initiator, (BASF), and 3 parts by weight of the binderprepared in Preparative Example 4 were added and diluted with methylethyl ketone, thereby preparing an adhesive composition (solid content:30 wt %).

The prepared adhesive composition was coated to a thickness of 13 μm ona primer coating surface of a polyethylene terephthalate (PET) film as abase film (SKC, thickness: 75 μm, with one surface subjected to urethaneprimer coating) and dried at 90° C. for 4 min. A release film(thickness: 25 μm, one surface subjected to silicone release treatment)was bonded to an adhesive layer and left at 50° C. for 2 days, therebypreparing an adhesive film-containing sheet in which the adhesive film(thickness: 13 μm) and the release film are sequentially stacked on thebase film.

Examples 2 to 7

Adhesive film-containing sheets were prepared by the same method as inExample 1 except that the kind and content of each component werechanged as listed in Table 2. In Table 2, “-” means that a correspondingcomponent was not used.

Comparative Examples 1 and 2

Adhesive film-containing sheets were prepared by the same method as inExample 1 except that the kind and content of each component werechanged as listed in Table 2.

Herein, among the components used in the Examples and ComparativeExamples, the mono- or higher functional monomers were as follows.

Monomer A: Lauryl acrylate

Monomer B: 1,6-hexanediol diacrylate

Monomer C: Benzyl acrylate

Monomer D: Ethylene glycol phenyl ether acrylate

Each of the adhesive film-containing sheets manufactured in the Examplesand Comparative Examples was evaluated as to the following propertiesand results are shown in Table 2.

(1) Initial peel strength (unit: gf/inch): The adhesive film was exposedby removing the release film from each of the adhesive film-containingsheets manufactured in the Examples and Comparative Examples. Apolyimide film (GF200, thickness: 50 μm, SKCKOLON) was adhered to theexposed surface of the adhesive film, compressed by a roller under aload of 2 kg, and cut into a specimen having a size of 25 mm×100 mm(width×length). FIG. 1A shows the prepared specimen. Referring to FIG.1A, a PET film 1, an adhesive film 2, and a polyimide film 3 aresequentially stacked. The specimen was left under conditions of 23±1° C.and 55±5% RH for 30 minutes. Peel strength was measured upon removal ofthe polyimide film from the adhesive film by a T-peel strengthmeasurement method using a tensile tester (Texture analyzer, TA IndustryCo., Ltd.) under conditions of peeling temperature: 25° C., peelingrate: 2,400 mm/min, and peeling angle: 180° in accordance with JISZ2037.T-peel strength may be measured with reference to FIG. 1B. T-peelstrength refers to peel strength upon peeling off the polyimide film 3from the PET film 1 and the adhesive film 2. T-peel strength wasmeasured by pulling the polyimide film 3 in an arrow direction of FIG.1B, with the PET film 1 and the adhesive film 2 secured to jigs of a TAinstrument.

(2) Peel strength after UV irradiation (unit: gf/inch): A specimen wasprepared by sequentially stacking a PET film, an adhesive film, and apolyimide film using the same method as in (1). The specimen wasirradiated at a PET film side thereof with UV light having a wavelengthof 385 nm at a dose of 1,000 mJ/cm² using a UV LED irradiator(SUV-L5160A, UVSMT Co., Ltd.) and was left under conditions of 23±1° C.and 55±5% RH for 30 minutes. Then, peel strength was measured uponremoval of the polyimide film from the adhesive film by a T-peelstrength measurement method using a tensile tester (Texture analyzer, TAIndustry Co., Ltd.) under conditions of peeling temperature: 25° C.,peeling rate: 2,400 mm/min, and peeling angle: 180° in accordance withJISZ2037.

(3) Peel strength after UV irradiation and heat treatment (unit:gf/inch): A specimen was prepared by sequentially stacking a PET film,an adhesive film, and a polyimide film using the same method as in (1).The specimen was irradiated at a PET film side thereof with UV lighthaving a wavelength of 385 nm at a dose of 1,000 mJ/cm² using a UV LEDirradiator (SUV-L5160A, UVSMT Co., Ltd.), held in an oven at 50° C. for20 minutes, and was then left under conditions of 23±1° C. and 55±5% RHfor 30 minutes. Then, peel strength was measured upon removal of thepolyimide film from the adhesive film by a T-peel strength measurementmethod using a tensile tester (Texture analyzer, TA Industry Co., Ltd.)under conditions of peeling temperature: 25° C., peeling rate: 2,400min/min, and peeling angle: 180° in accordance with JISZ2037.

TABLE 2 Example Comparative Example 1 2 3 4 5 6 7 1 2 (Meth)acrylic KindPrepar- Prepar- Prepar- Prepar- Prepar- Prepar- Prepar- Prepar- Prepar-copolymer ative ative ative ative ative ative ative ative ative Example1 Example 1 Example 1 Example 1 Example 2 Example 3 Example 1 Example 1Example 1 Content 100 100 100 100 100 100 100 100 100 Curing Isocyanate-0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 agent based Metal 0.3 0.3 0.3 0.30.3 0.3 0.3 0.3 0.3 chelate- based Mono- Kind Monomer Monomer MonomerMonomer Monomer Monomer Monomer Monomer Monomer or higher A B C D C C CA C functional Content 80 80 50 50 50 50 50 80 50 monomer BinderPreparative 3 3 3 3 3 3 — — — having a Example 4 melting Preparative — —— — — — 3 — — point of Example 5 30° C. to 60° C. Initiator 0.5 0.5 0.50.5 0.5 0.5 0.5 0.5 0.5 Curing accelerator 0.2 0.2 0.2 0.2 0.2 0.2 0.20.2 0.2 Initial peel strength 68 57 48 53 51 57 52 77 65 Peel strengthafter 230 302 327 345 262 293 334 233 323 UV irradiation Peel strengthafter 524 531 721 798 694 705 752 289 354 UV irradiation and heattreatment Equation 1 7.7 9.3 15.0 15.1 13.6 12.4 14.5 3.7 5.4

As shown in Table 2, the adhesive films according to embodiments of thepresent invention had an initial peel strength of greater than 0 gf/inchto 100 gf/inch. Accordingly, although not shown in Table 2, the adhesivefilms could be easily removed from the adherend. The adhesive filmaccording to embodiments of the present invention had a peel strengthincrease rate of 7.0 or more, as calculated by Equation 1. As a result,the adhesive film secured to the adherend could improve adhesivestrength and durability of an optical member including the adherend.Accordingly, the adhesive film according to embodiments of the presentinvention could be concurrently (e.g., simultaneously) used as atemporary protective film for processes with respect to a flexible panelsubstrate and as a protective film for pattern reinforcement, which isselectively partially removed to form patterns. Further, it could beconfirmed that peel strength of the adhesive film according toembodiments of the present invention was remarkably increased after UVirradiation and heat treatment, as compared with peel strength of theadhesive film after UV irradiation.

Accordingly, embodiments of the present invention provide an adhesivefilm that can be easily removed from an adherend after attachment of theadhesive film thereto and can be secured to the adherend through aprocess (e.g., a predetermined process). Further, embodiments of thepresent invention provide an adhesive film that can be adhered at lowpeel strength to an adherend to provide temporary protection to theadherend in an initial stage and can be easily removed from the adherendwithout deformation and/or damage to the adherend through selectivecutting of an unnecessary portion thereof. Further, embodiments of thepresent invention provide a protective adhesive film that exhibitssignificant increase in peel strength after irradiation with light andheat treatment, as compared with peel strength before irradiation withlight, and is secured to an adherend to improve durability of an opticalmember including the adherend. Further, embodiments of the presentinvention provide an adhesive film that can be concurrently (e.g.,simultaneously) used as a temporary protective film for processes withrespect to a flexible panel substrate and as a protective film forreinforcement of patterns, which is selectively partially peeled off toform patterns.

Conversely, the adhesive films of the Comparative Examples failing tosatisfy the features of the present invention did not have the effectsof the present invention.

It should be understood that various modifications, changes,alterations, and equivalent embodiments can be made by those skilled inthe art without departing from the spirit and scope of the presentinvention.

What is claimed is:
 1. An adhesive film formed of an adhesivecomposition comprising a (meth)acrylic copolymer, a curing agent, amono- or higher functional monomer, a binder having a melting point ofabout 30° C. to about 60° C., and an initiator, the adhesive film havinga peel strength increase rate of 7.0 or more, as calculated by thefollowing Equation 1:Peel strength increase rate=P2/P1, where P1 is an initial peel strength(unit: gf/inch) of the adhesive film with respect to an adherend, asmeasured on a specimen of the adhesive film and the adherend, and P2 isa peel strength of the adhesive film (unit: gf/inch) with respect to theadherend, as measured on the specimen of the adhesive film and theadherend after irradiation with light and heat treatment of thespecimen.
 2. The adhesive film according to claim 1, wherein P1 isgreater than 0 gf/inch and less than or equal to about 100 gf/inch. 3.The adhesive film according to claim 1, wherein P2 is about 500 gf/inchor more.
 4. The adhesive film according to claim 1, wherein the mono- orhigher functional monomer has a higher glass transition temperature in ahomopolymer phase than the (meth)acrylic copolymer.
 5. The adhesive filmaccording to claim 1, wherein a difference in glass transitiontemperature between the mono- or higher functional monomer in ahomopolymer phase and the (meth)acrylic copolymer is about 20° C. ormore.
 6. The adhesive film according to claim 1, wherein the mono- orhigher functional monomer has a glass transition temperature of about−30° C. or more in a homopolymer phase.
 7. The adhesive film accordingto claim 1, wherein the mono- or higher functional monomer comprises anaromatic group-containing mono- or higher functional monomer.
 8. Theadhesive film according to claim 7, wherein the aromaticgroup-containing mono- or higher functional monomer comprises a compoundof the following Formula 1:

where R¹ is hydrogen or a methyl group; s is an integer of 0 to 10; R²is a substituted or unsubstituted C₆ to C₅₀ aryl group or a substitutedor unsubstituted C₆ to C₅₀ aryloxy group; and T is a substituted orunsubstituted C₁ to C₆ alkylene group or a substituted or unsubstitutedC₁ to C₆ alkyleneoxy group.
 9. The adhesive film according to claim 1,wherein the mono- or higher functional monomer is present in an amountof about 10 parts by weight to about 200 parts by weight relative to 100parts by weight of the (meth)acrylic copolymer.
 10. The adhesive filmaccording to claim 1, wherein the (meth)acrylic copolymer has a glasstransition temperature of about −10° C. or less.
 11. The adhesive filmaccording to claim 1, wherein the (meth)acrylic copolymer comprises acopolymer of a monomer mixture comprising an alkyl group-containing(meth)acrylic monomer and a hydroxyl group-containing (meth)acrylicmonomer, the hydroxyl group-containing (meth)acrylic monomer beingpresent in an amount of about 0.1 mol % to about 10 mol % in the monomermixture.
 12. The adhesive film according to claim 1, wherein the curingagent comprises a mixture of an isocyanate curing agent and a metalchelate curing agent.
 13. The adhesive film according to claim 1,wherein the binder having a melting point of about 30° C. to about 60°C. comprises a binder of a monomer mixture comprising a (meth)acrylatehaving a linear or branched C₁₆ to C₂₂ alkyl group at an ester site. 14.The adhesive film according to claim 13, wherein the monomer mixturefurther comprises at least one selected from among a (meth)acrylatehaving a linear or branched alkyl group containing ten or fewer carbonatoms at an ester site and a silicone-modified mono-functional(meth)acrylate.
 15. The adhesive film according to claim 1, wherein theinitiator comprises at least one selected from among a photo-radicalinitiator and a photo-cationic initiator.
 16. The adhesive filmaccording to claim 1, wherein the adhesive composition comprises 100parts by weight of the (meth)acrylic copolymer, about 0.01 parts byweight to about 8 parts by weight of the curing agent, about 10 parts byweight to about 200 parts by weight of the mono- or higher functionalmonomer, about 0.1 parts by weight to about 20 parts by weight of thebinder having a melting point of about 30° C. to about 60° C., and about0.01 parts by weight to about 7.5 parts by weight of the initiator. 17.An optical member comprising a flexible panel and an adhesive filmstacked on at least one surface of the flexible panel, wherein theadhesive film comprises the adhesive film according to claim
 1. 18. Theoptical member according to claim 17, comprising: the flexible panelcomprising a flexible substrate, the adhesive film stacked on a lowersurface of the flexible substrate, and a protective film stacked on alower surface of the adhesive film.
 19. An optical display apparatuscomprising the adhesive film according to claim
 1. 20. An adhesive filmformed of an adhesive composition comprising a (meth)acrylic copolymer,a curing agent, a mono- or higher functional monomer, a binder having amelting point of about 30° C. to about 60° C., and an initiator, theadhesive film having an initial peel strength of greater than 0 gf/inchto about 100 gf/inch with respect to an adherend, as measured on aspecimen of the adhesive film and the adherend, and a peel strength of500 gf/inch or more with respect to the adherend, as measured on thespecimen of the adhesive film and the adherend after irradiation withlight and heat treatment of the specimen.